The leaders of the world’s largest economies were expected to reaffirm their commitment to climate change action when they convened this weekend in Germany for the annual G20 summit. Or, at least most were expected to.

How President Donald Trump will act is far from clear, and not only because he is unpredictable. He’s said he’s willing to stick with the Paris accord on terms more favourable to the U.S., but has also warned America could walk away entirely. So it’s an open question what path the U.S. will now take. The Republican leadership may not truly want a better deal — either because they don’t think climate change is happening, or because they don’t think tackling it to be worth the costs. But if they are sincere, they should recognize that the pursuit of an effective international climate accord is the only rational course of action.

The GOP should recognize that an effective international climate accord is the only rational course of action

Indeed, this has actually been the logic of conservative leaders for some time now. Back in 2001, President George W. Bush claimed his administration took climate change “very seriously,” but could not support Kyoto “because it exempts 80 percent of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the U.S. economy.” Prime Minister Stephen Harper used to say Canada was prepared to sign on to an international climate agreement, or to implement a carbon tax, just so long as it wouldn’t put Canada out of step with the world’s major economies.

In effect, Bush and Harper’s comments spoke to the “collective action” dilemma that’s at the heart of the climate change problem, and which makes solutions so hard to come by. That is: states have little incentive to reduce their emissions so long as others are not also doing so. By the same token, the implicit promise of Trump, Bush, Harper and others has been that they can support coordinated environmental action so long as advanced nations aren’t the ones doing all the work.

And for all its flaws, the Paris agreement can—from this perspective—be viewed as at least a partial accomplishment. Whereas the Kyoto Protocol that it replaces requires only developed nations to meet binding emission targets (while exempting developing nations), Paris was about getting all emitters on board. In this, the negotiators succeeded. Before the U.S. withdrew, Paris had the buy-in of all the world’s major emitters—a feat anything but assured going in, and nothing to be sneezed at.

Of course, to get this near-universal buy-in, Paris ended up becoming a very watered-down agreement. It does suffer from all the shortcomings its critics now accuse it of: non-binding emissions targets; impunity for non-compliance; allowing heavy emitters like China to put off emissions reductions well into the future.

Before the U.S. withdrew, Paris had the buy-in of all the major emitters - a feat anything but assured going in

But Paris is also not the last word on this subject. It’s likely a mere stepping-stone to future, firmer agreements. Global climate negotiations have only been seriously underway for 25 years, and already in this short period have undergone four phases of negotiations: the United Nations Framework Convention on Climate Change in 1992; the Berlin mandate in 1995; Kyoto in 1997; and Paris in 2016. Each built on the lessons of the past.

So if Trump is sincere about wanting the U.S. to be the “world’s leader in environmental protection,” it would be irrational to forgo an international agreement like Paris (or any successor to it) in favour of going it alone. Moreover, odds are, America could enjoy the political benefits of participation in a global climate accord, without having to incur inordinate costs. According to some projections, the U.S. might be on track to meeting the emission targets it had committed to under Paris, anyway, because America’s fracking revolution has natural gas displacing emissions-intensive coal power, and because of state-level initiatives.

Thus, if the Republicans do forgo the climate agreement they say they want, it’ll finally reveal what their rhetoric was all about: a strategy for doing nothing, dressed up in smart language about economics and international law.